[sidemouse.ii]

Either the coils, or possibly ...

I had a persistent problem on a mower with a V-twin Kawasaki, long story short it turned out one of the plastic pieces that holds the throttle / choke linkage was cracked... In my case it was the choke linkage, the crack made it so the engine would choke fine but it wouldn't unchoke completely and thus as soon as it warmed up I'd lose power.

Specifically the metal rods that connect to the carburetor, when one of these plastic pieces breaks or is cracked it may still be connected but it's no longer operating the way it should... It's worth checking these up close visually, perhaps move the linkages by hand (you may have to operate the choke / throttle lever) to ensure smooth operation.

 

[sidemouse.ii]

He put a new carb on it.......Even if he did have the plastic connectors on the original carb, it would not kill the engine......Just make it harder to start..

Might be the choke linkage closes good, but it doesn't open completely...
Then it will start fine, and as soon as it warms up it loses power.
If a linkage is loose often the choke can be adjusted enough to still close...
But once you get moving the play in the linkage allows for play in the choke valve, and that play allows the plate to close even partially it cuts the air flow and thus power.

The linkage pieces in my carb are metal and are working fine. The choke does not get stuck and is working fine.
I also replaced the solenoid in the picture.
Thanks.

On the metal ones, inside the hole where the linkage hooks to the carburetor there is a hard plastic grommet piece or there should be... That was the problem I had, the little hard plastic grommet inside that hole was cracked and allowing linkage play. It was so minor, took me literally years to track it down.

I did the same as you, both coils, valves, fuel lines and filter, cleaned up underneath the covers real good... I was at wits end. I took it to a repair shop twice and it didn't act up when I was there, not even driving it around and engaging the blades but take it out to mow for a day and I couldn't even finish the first yard.
I replaced gas caps too, thinking if a gas cap vent was clogged.

When I replaced the carburetor...
Which at this stage I was just replacing parts, but it came with the new plastic pieces.
That's when I saw the problem.

Linkages on these things...

Here's the old thread on that FH721V:

FH721V suddenly started struggling

On my ztr today... I adjusted the valves about 1-2 years ago... It ran good for quite a while, but today while going up an incline it suddenly lost power. It will run "all right" without load but it does pop and sputter a little. Engage the blades and it pops and misses just a little more...

www.lawnsite.com

It would start awesome, run good for a few minutes and then the nonsense would start...

 

[sidemouse.ii]

If there is one thing I am sure of is that the problem is not the choke. It works perfect, nothing cracked on the linkages. If it was choke related the engine would begin to run rough, but the engine runs smooth, warms up and dies under load.
Thanks.

Cool.
You might still want to read through that FH721v thread, it covers quite a few possible causes to do with the "cuts off / loses power once warmed up," the one thing I regret ... Which didn't end up being the problem anyway, but when I was adjusting the valves I should've pulled the pushrods and checked them for straightness because there's a documented issue in that direction as well.

 

[sidemouse.ii]

So you had an engine that kept blowing crankshaft seals and to replace it you bought a used engine from someone who stated it "ran great but keeps blowing head gaskets..." I am not sure I would label an engine that keeps blowing head gaskets as a "great runner" but let me leave that for another discussion.

Common issues with the FH721 and related series engines is overheating due to clogged or plugged cooling systems, the problems associated with overheating (such as warped heads) and loose valve guides which can result in bent pushrods, blown head gaskets and so on.

Granted, this wouldn't cause it to die like it was shut off ...
If you want to go further into the overheating discussion I can do so, but it relates more to a mower that struggles under load... It will die if you push it and engaging a PTO will certainly do that, but if you disengage immediately it should recover even if sluggishly which would lead me to further search in the areas of overheating due to crud buildup and loose valve guides and warped heads and such... But again even with a warped head it would still run warmed up, it just won't run good.

So perhaps the issue is electrical, perhaps a wire is shorting out against the frame someplace but then wouldn't it do the same when cold? Might be worth looking underneath at the clutch connector... If that comes loose or if it has 3 wires and (I think) the ground wire is disconnected then it will kill the mower when engaging the clutch but also when moving the stick(s) because of the logic circuitry, still odd that it won't do it when it's cold...

Which leads me back to the ignition coils.
You stated you replaced these, if I recall correctly.

 

[sidemouse.ii]

Wow, a lot to think about here. I have tried to disengage the pto right away and it still dies.
I got new coils yesterday. I had checked spark before and have spark on both cylinders, but I don't know if a coil that is failing can recover that quickly.
I am going to check disconnecting the kill wire first, then removing the fuel shutoff solenoid to see if it still happens and go on from there.
Thanks again.

That is good. Often these V-twins can run without load on one cylinder and the operator barely notices, but as soon as a load gets put on the story changes. To test coils we can do so before ordering new ones, do this with the engine off:
Disconnect either side spark plug wire, then start the mower.
See if it runs, even if crappy.
If it does, cut it off, reconnect whichever side and unplug the other side.
See if it runs again.
If it won't run on either side then your faulty coil is the one that's still connected.
Granted, it is recommended to replace both coils at the same time.
This is also something where I just might use the coils off an old engine if it's the same part number.

On another note, aftermarket carburetors for the FH721V run just under $35...
One of these comes with all the gaskets (even some you won't need), and the linkage connectors:

Carburetor Kawasaki (15004-0757,15003-7094, 15004-1005) FH721V for sale | eBay

Get the best deals for Carburetor Kawasaki (15004-0757,15003-7094, 15004-1005) FH721V at eBay.com. We have a great online selection at the lowest prices with Fast & Free shipping on many items!

www.ebay.com

I replaced the one on mine with that one, I would suggest replacing all the cheaper parts (under $100) one at a time before tearing into the cylinder head to replace a gasket. So that would be coils and carburetor, I think you've replaced the rest of things, might check that black rubber breather / PCV tube as well.

 

[sidemouse.ii]

Good to know.
The wiring diagram shows the oil pressure switch is connected to the carburetor fuel solenoid switch. Could it be telling me that I have low oil pressure?

Hmmm...
How was it running before you swapped carburetors?

 

[sidemouse.ii]

You're frustrated because you won't even do the first thing in trouble shooting your engine. You were asked to test the coils on the second post of this thread. You still haven't done that and we still don't know what's wrong. This is why the few here that help others with correct diagnoses have problems with backyard mechanics that have no idea the correct way to diagnose the problems that we have trained and worked with for many years experience. Yes we make mistakes and aren't always correct but the problem is not right in front of us to diagnose. Eyes, ears and smells are part of our trouble shooting that we do not have in this situation. All we ask is that the person with the problem follow through with the very simple tests that we ask to help them fix their piece of equipment before jumping threw hoops from people guessing with all these crazy ideas that might be causing the problems.
My rant is over. Good luck with changing all the unneeded parts to your engine.

Right...
The solution is in any one of ten or twelve or so possible causes but the only way anyone would ever get to the bottom of it is to make a list... I suggest going in order of cheapest / easiest first but make a list, and then start at the top of the list and go through each and every one. Test and / or replace parts and do it one at a time and don't jump around and stick to the list until we find the problem, and if it takes time but if people aren't willing to test and do things in some kind of an order then there's not a whole lot any one of us can do about it.

Also never pull a carburetor without having the new gaskets handy.
Just certain rules some of us have learned to live by.

 

[sidemouse.ii]

Changing parts to determine why an engine is not working properly can get expensive fast.

Time is worth money, too.
At $80 an hour even diagnostic work gets expensive.
Once we value our time it gives us perspective in terms of whether we want to diagnose, or just replace.

Remember that only 3 basics needed to run many gas engines
Combustion air
Gas
Spark
Removing any of these 3 and u will have a none running engine

Yeah but this one runs, it just cuts off once it's warmed up and the operator engages the PTO or the forward/reverse hydraulics... So the first step here would be to test the coils, come to think of it maybe the seat safety switch.

 

[sidemouse.ii]

Ok, I took a video after changing the coils.

But now I notice the engine surging when warm after I restart it.
One question. WillI I hurt the engine if I run it with a bad head gasket?

While the rear bumper is off
I would either replace the carburetor with a new one, buy the gaskets as well.
Or adjust the valves next, you'll need the valve cover gaskets:
110607013 Gasket, Rocker case

One question. WillI I hurt the engine if I run it with a bad head gasket?

It's not good for it, but you should be able to run it like you're doing for testing.

 

[sidemouse.ii]

Point is, if you truly value your time, you learn to recognize where your time is best spent.

 

[sidemouse.ii]

That's too bad really, seen many a good engine get thrown away over what is most likely a minor issue. I do agree throwing used parts at something broken isn't likely to produce a good fix.
Typical quick determination through notoriously inaccurate methods, yup it's toast, here buy another. Granted time is money too.